1. Field of the Invention
The invention relates in general to a signal receiving circuit and method, and more particularly, to a signal receiving circuit and method that adjusts a sampling clock according to an error of the sampling clock, and a circuit and method for calculating an error of a sampling clock.
2. Description of the Related Art
FIG. 1 shows a schematic diagram of a conventional signal transmission process from a transmitter to a receiver. A signal x(t) is sent from the transmitter, and passes through a channel to form a signal y(t) at the receiver. The equation is as follows: y(t)=x(t)h(t)+w(t), where h(t) represents a multipath fading channel function, and w(t) represents an additive white Gaussian noise (AWGN) function. When x(t) is a multicarrier signal, x(t) can be represented as
            x      ⁡              (        t        )              =                  ∑                  k          =                      -            ∞                                    k          =          ∞                    ⁢                          ⁢                        I          k                ·                  P          ⁡                      (                          t              -                              kT                                  sym                  ,                  tx                                                      )                                ,where Ik is the kth symbol, P(t) is a pulse shaping function, and Tsym, tx is a symbol period at the transmitter.
At the receiver, after sampling the signal y(t) by a sampling speed 1/Tsam, a series of data signals y(m)=y(t)↑t=m·Tsam are formed. The data signals y(m) are processed by a timing recovery circuit 110 to obtain data signals y(n). The timing recovery circuit 110 down-samples the data signals y(m) by a frequency (i.e., 1/Tsym, tx) corresponding to the symbol period Tsym, tx of the transmitter, such that the sampling clocks at the receiver and the transmitter may be synchronized to restore data originally sent from the transmitter. However, the above description gives an ideal situation. Due to circuit production factors, the frequency of the sampling clock at the transmitter is not entirely equal to 1/Tsym, tx. As the receiver does not know the exact sampling clock frequency at the transmitter, the sampling clock frequency at the receiver cannot be set to be identical to that at the transmitter. Further, a frequency previously properly set may change on account of operation environmental factors. As a result, the data signals eventually received by the receiver are y(n)=y(t)|t=n·Tsym,rx, where Tsym, rx is a symbol period at the receiver, and Tsym, rx≠Tsym, tx. Even a minute difference between the two results in data errors over a long period of time.